Copper Complexation Capacity Research Articles

Copper Complexing Capacity and Trace Metal Content in Common and Balsamic Vinegars: Impact of Organic Matter

Complex formation is among the mechanisms affecting metal bioaccessibility. Hence, the quantification of organic metal complexation in food items is of interest. Organic ligands in solutions of environmental and/or food origin function as buffering agents against small changes in dissolved metal concentrations, being able to maintain free metal ion concentrations below the toxicity threshold. Organic matter in vinegars consists of bioactive compounds, such as polyphenols, Maillard reaction endproducts, etc., capable of complexing metal ions. Furthermore, transition metal ions are considered as micronutrients essential for living organisms exerting a crucial role in metabolic processes. In this study, differential pulse anodic stripping voltammetry (DPASV), a sensitive electrochemical technique considered to be a powerful tool for the study of metal speciation, was applied for the first time in vinegar samples. The concentrations of Cu complexing ligands (LT) in 43 vinegars retailed in Greece varied between 0.05 and 52 μM, with the highest median concentration determined in balsamic vinegars (14 μM), compared to that of common vinegars (0.86 μM). In 21% of the vinegar samples examined, LT values were exceeded by the corresponding total Cu concentrations, indicating the presence of free Cu ion and/or bound within labile inorganic/organic complexes. Red grape balsamic vinegars exhibited the highest density of Cu ligands per mass unit of organic matter compared to other foodstuffs such as herbal infusions, coffee brews, and beers. Among the 16 metals determined in vinegars, Pb is of particular importance from a toxicological point of view, whereas further investigation is required regarding potential Rb biomagnification.

An automatic titration setup for the chemiluminometric determination of the copper complexation capacity in opaque solutions

An automatic titration setup exploiting flow analysis was proposed for the evaluation of the copper complexation capacity of highly opaque substances (milk and humic substances). The binary search approach was implemented in a flow-batch analyzer, in order to add the in-line selected titrant (e.g. copper ions) volumes to the sample. When the titration end-point was surpassed, the free metal ions catalyzed the reaction of luminol with hydrogen peroxide, yielding the chemiluminescence, which was quantified even in solutions of high opacity. Accuracy was assessed through addition/recovery tests involving classical complexing species (EDTA, DTPA and DTTC), and recoveries ranged from 96% to 115%. The proposed system requires low amounts of reagents and samples (0.42 mg of luminol, 82 μg H2O2, 1.10 mL of sample) per titration run, meaning ca. 12 mL of effluent per titration, and yields precise results (5% r.s.d.) at a sampling throughput of 43 h−1.

Copper Complexation by Dissolved Organic Matter in arid Soils: A Voltametric Study

A voltammetric method was used to estimate the complexing capacity of water extracts from both desert soils sampled at the root zone of creosote and salt cedar plants, and in soils from interspace or background regions where no vegetative influence was apparent. The copper complexing capacity of water extracts of these desert soils was influenced by contact time and pH. In soils from the root zones of creosote and salt cedar plant, copper complexation capacities at pH 8 were from 5 µM to 60 µM after five min contact periods, while 18 h contact periods yielded copper complexation capacities of 40 µM–80 µM. Soils with no vegetative influence had copper complexing capacities of less the 2 µM. The copper complexing capacities of these soils are well correlated with the concentration of organic carbon in the water extract (r2 = 0.86). The abundance of soluble organic matter in the root zone of desert shrubs has the potential to control the solution speciation of Cu2+. The formation of soluble complexes should also have an important influence on the plant uptake and transport of copper, as well as other heavy metals in the root zones of desert shrubs and beyond.

Applicability Comparison and Application Study of Two Methods for Determination of the Copper Complexing Capacity of Waters

Complexing capacity (CC) is an important indicator affecting the environmental behavior of heavy metals in water, which can be determined by different methods based on different mechanisms. To validate and compare the applicability of different methods in CC determination, the complexing capacity of Cu2+ (CuCC) in solutions of ethylenediamine tetraacetic acid (EDTA) and acesulfame was determined by methods of dithizone extraction kinetics (DEK) and ion-selective electrodes (ISE), while EDTA and acesulfame were selected to represent strong and weak ligands in water, respectively. DEK method was found to be more suitable for determining the contribution of strong ligands to CuCC, while the results determined by ISE were related to both the strong and weak ligands in water. DEK and ISE methods were used to measure CuCC of several actual water samples, including samples from reservoir, discharge river, fishpond, and landfill leachates. CuCC in the water samples of the reservoir and discharge river measured by ISE were 86.9-227.0 μmol·L-1, which were about one order of magnitude higher than those measured by DEK (9.9-14.6 μmol·L-1). For the landfill leachates, CuCC measured by ISE were 6998.4-31005.8 μmol·L-1, which were 2 orders of magnitude higher than those by DEK (89.6-109.1 μmol·L-1). The increase of CuCC in the polluted water samples might be due to the weak ligands like pollutants. A positive correlation (R=0.975, P<0.01) was found between the CuCC related to the weak ligands (ΔCuCC) and the sum concentration of ammonia nitrogen and organic nitrogen in waters.

Copper(II) and Nickel (II) Complexation Capacity of Dissolved Organic Matter from Rivers of Agricultural and Urban Areas in the State of São Paulo

This study had as main objective to determine the complexing ability of the Organic Matter (OM) from typical agricultural areas and from urban areas with copper and nickel ions. The samples were collected during the dry and rainy seasons and were subjected to study the complexing capacity and OM conditional stability constant with Cu(II) and Ni(II) ions using a luminescence spectrofluorometer and tangential flow ultrafiltration system. The conditional stability constant values (log Kc) of OM with the copper ion varied from 0.04 to 1.35 with the highest value obtained for the place with the largest dissolved organic carbon (DOC 2.73-2.43 mg L-1) and the lowest for the smallest site DOC, corroborating the degree of aromaticity. We can conclude that the Dissolved Organic Matter (DOM) of the bodies of water in agricultural and urban areas contained a lower number of binding sites when compared with other locations.

Impacts of Microbial Activity on the Optical and Copper-Binding Properties of Leaf-Litter Leachate

Dissolved organic matter (DOM) is a universal part of all aquatic systems that largely originates with the decay of plant and animal tissue. Its polyelectrolytic and heterogeneous characters make it an effective metal-complexing agent with highly diverse characteristics. Microbes utilize DOM as a source of nutrients and energy and their enzymatic activity may change its composition, thereby altering the bioavailability and toxicity of metals. This study investigated the impacts of microbial inoculation upon the optical and copper-binding properties of freshly produced leaf-litter leachate over 168 h. Copper speciation was measured using voltammetry, and using fluorescence quenching analysis of independent fluorophores determined using parallel factor analysis (PARAFAC). Two protein/polyphenol-like and two fulvic/humic-like components were detected. Thirty-five percent of total protein/polyphenol-like fluorescence was removed after 168-h of exposure to riverine microbes. The microbial humic-like and tryptophan-like PARAFAC components retained significantly different log K values after 168 h of incubation (p < 0.05), while their complexing capacities were similar. Using voltammetry, a sixfold increase in copper-complexing capacity (CC, from 130 to 770 μmol Cu g C−1) was observed over the exposure period, while the conditional binding constant (log K) decreased from 7.2 to 5.8. Overall binding parameters determined using voltammetry and fluorescence quenching were in agreement. However, the electrochemically based binding strength was significantly greater than that exhibited by any of the PARAFAC components, which may be due to the impact of non-fluorescent DOM, or differences in the concentration ranges of metals analyzed (i.e., different analytical windows). It was concluded that the microbial metabolization of maple leaf leachate has a significant impact upon DOM composition and its copper-binding characteristics.

Copper complexation capacity in surface waters of the Venice Lagoon

Total copper (Cu T), copper ion activity (pCu) and the copper complexation capacity (CuCC) were determined in samples of seawater collected in July 2003 from the Venice Lagoon. Cu T and CuCC showed considerable spatial variability: Cu T ranged from 1.8 to 70.0 nM, whereas the CuCC varied from 195 to 573 nM. pCu values varied from 11.6 to 12.6 and are consistent with those previously reported in estuarine and coastal areas (10.9–14.1). The range of Cu T values compares well with those reported in the past in the lagoon and in the adjacent Adriatic Sea. The highest concentrations of Cu T were found in samples collected near the industrial area of Porto Marghera, whereas the lowest were measured near the Chioggia and Malamocco inlets, where an intense tidally-driven renewal of seawater takes place. Although CuCC showed a high degree of spatial variability, the values recorded in the Venice Lagoon are comparable to those reported in other estuarine systems. In addition, CuCC was positively correlated with dissolved organic carbon (DOC), suggesting that organic ligands responsible for Cu complexation are part of the bulk organic matter pool in the lagoon. The CuCC:Cu T molar ratio was, on average 55:1, indicating that a large excess of complexation capacity exists in the Venice Lagoon. The high levels of CuCC and the narrow range of pCu indicates the importance of the role played by organic ligands in controlling the free ion Cu concentrations in the lagoon, and as a consequence, regulating its availability and/or toxicity.

Effect of copper sulphate treatment on natural phytoplanktonic communities

Copper sulphate treatment is widely used as a global and empirical method to remove or control phytoplankton blooms without precise description of the impact on phytoplanktonic populations. The effects of two copper sulphate treatments on natural phytoplanktonic communities sampled in the spring and summer seasons, were assessed by indoor mesocosm experiments. The initial copper-complexing capacity of each water sample was evaluated before each treatment. The copper concentrations applied were 80 μg l −1 and 160 μg l −1 of copper, below and above the water complexation capacity, respectively. The phytoplanktonic biomass recovered within a few days after treatment. The highest copper concentration, which generated a highly toxic environment, caused a global decrease in phytoplankton diversity, and led to the development and dominance of nanophytoplanktonic Chlorophyceae. In mesocosms treated with 80 μg l −1 of copper, the effect on phytoplanktonic community size-class structure and composition was dependent on seasonal variation. This could be related to differences in community composition, and thus to species sensitivity to copper and to differences in copper bioavailability between spring and summer. Both treatments significantly affected cyanobacterial biomass and caused changes in the size-class structure and composition of phytoplanktonic communities which may imply modifications of the ecosystem structure and function.

Photodegradation of strong copper-complexing ligands in organic-rich estuarine waters

Exposure to solar radiation substantially decreased the strong copper-complexing capacity of samples collected from the organic-rich Cape Fear estuary, North Carolina. Samples exposed to natural sunlight for 1-2 d experienced a loss of strong Cu ligand (modeled at fixed K‘CuL = 1013.5) ranging from 15-33%, and >90% using long-term exposures under controlled conditions with a Xe arc solar simulator light (14 d summer sunlight). Pseudo firstorder rate constants of strong Cu ligand photodegradation averaged 0.28 d-1 for two separate Cape Fear samples exposed to simulated solar radiation, much higher than corresponding dissolved organic carbon photooxidation rate constants (<0.01 d-1). Degradation rates measured in solar simulator experiments predicted ligand concentrations in separate samples exposed to natural sunlight within 30% after rates were normalized to the ultraviolet (UV) light absorption coefficient at 300 nm. UV light is not solely responsible for photodegradation because exposure to photosynthetically active radiation also decreased strong Cu ligand levels, but with a smaller rate constant (0.06 d-1). Although photodegradation appears to be a relatively minor sink within the Cape Fear estuary because of a shallow light penetration depth (<2% of water column) and short residence times (<1 week), strong Cu ligand levels in optically clearer South Atlantic Bight (SAB) surface waters are likely to be substantially reduced by photodegradation. Ligand degradation may be especially important to Cu-sensitive ecosystems where large increases in bioavailable and potentially toxic levels of free Cu2+ ions are possible.

Copper Complexing Capacity of Throughfall and its Environmental Effect

Copper complexing capacity (CuCC) and conditional stability constants (K′) of the complexes were analyzed for throughfall collected in Japanese cypress (Chamaecyparis obtusa), Japanese cedar (Cryptomeria japonica), Japanese red pine (Pinus densiflora), and bamboo-leafed oak (Quercus myrsinaefolia) groves (soil: light-colored Andosol) located in a suburban area of Japan (Tsukuba, Ibaraki). The method was based on the titration of throughfall samples with standard Cu2+ solution using a Cu2+-selective electrode, followed by data analysis using the van den Berg-Ruzic plot (1:1-type complexes were assumed). CuCCs (μM) obtained were in the order: C. obtusa (7.1± 5.1) ≤ C. japonica (9.6± 5.6) < P. densiflora (15.9± 16.4) < Q. myrsinaefolia (29.3± 23.9). In addition, ratios of CuCC/DOC (μmol mg−1 C) were in the order: C. obtusa (0.42± 0.26) ≅ C. japonica (0.42± 0.22) ≅ P. densiflora (0.55± 0.38) ≪ Q. myrsinaefolia (2.0± 1.3), and the ratios in the throughfall of Q. myrsinaefolia were about 4 times higher than those in the throughfall of other tree species. On the other hand, log K′ was almost the same for all tree species (about 5.5). CuCC and also CuCC/DOC increased in spring and autumn, and decreased in summer and winter, indicating that organic matter with metal complexing capacity, released from trees, changed seasonally not only in quantity but also in quality. Since throughfall accelerated the leaching of metals from grove soil and artificial material (e.g. alloy) placed in the groves, it may be involved in the behavior of metals in the plant-soil ecosystem.

Copper Toxicity to Larval Stages of Three Marine Invertebrates and Copper Complexation Capacity in San Diego Bay, California

Temporal and spatial measurements of the toxicity (EC50), chemical speciation, and complexation capacity (Cu-CC) of copper in waters from San Diego Bay suggest control of the Cu-CC over copper bioavailability. While spatial distributions of total copper (CuT) indicate an increase in concentration from the mouth toward the head of San Diego Bay, the distribution of aqueous free copper ion (Cu(II)aq) shows the opposite trend. This suggests that the bioavailability of copper to organisms decreases toward the head of the bay, and is corroborated by the increase in the amount of copper needed to reach an EC50, observed for larval stages of three marine invertebrates (Mediterranean mussel, Mytilus galloprovincialis, sand dollar, Dendraster excentricus, and purple sea urchin, Strongylocentrotus purpuratus), and by the increase in Cu-CC heading into the head of the bay. The amount of Cu(II)aq required to produce a 50% reduction in normal larval development (referred to here as pCuTox,) of the mussel, the most sensitive of the three marine invertebrates, was generally at or above approximately 1 x 10(-11) mol L(-1) equivalents of Cu (i.e., pCuTox approximately 11 = -(log [Cu(II)aq])). These results suggest that the copper complexation capacity in San Diego Bay controls copper toxicity by keeping the concentration of Cu(II)aq at nontoxic levels.

Comparability of copper complexation capacity determination by absorption by chelating resin column and cathodic stripping voltammetry

A simple method has been developed for the determination of copper complexation capacity. It is based on absorption of non-complexed species on a chelating resin column. The limit of detection is for complexation equivalent to 3 μg Cu l −1 and the relative standard deviation of results is 10%. The method has been shown to be of comparable performance with voltammetric techniques in respect of the ligands detected. The approach offers the possibility of use in the field and of application to the determination of the speciation of other divalent trace metals.

Tangential-flow ultrafiltration: a versatile methodology for determination of complexation parameters in refractory organic matter from Brazilian water and soil samples.

In this work the copper(II) complexation parameters of aquatic organic matter, aquatic and soil humic substances from Brazilian were determined using a new versatile approach based on a single-stage tangential-flow ultrafiltration (TF-UF) technique (cut-off 1 kDa) and sensitive atomic spectrometry methods. The results regarding the copper(II) complexation capacity and conditional stability constants obtained for humic materials were compared with those obtained using direct potentiometry with a copper-ion-selective electrode. The analytical procedure based on ultrafiltration is a good alternative to determine the complexation parameters in natural organic material from aquatic and soil systems. This approach presents additional advantages such as better sensibility, applicability for multi-element capability, and its possible to be used under natural conditions when compared with the traditional ion-selective electrode.

Copper complexation capacity in waters and effluents – limitations of using DOC or colour as general predictors

It has been proposed that measures of organic carbon might be used to predict complexation capacity. The relationship between dissolved organic carbon, colour (absorbance at 400nm) and copper complexation capacity has been examined. Comparisons of data for surface freshwaters collected from 28 sites in England show no significant correlation. For estuarine samples, it seems that colour and complexation capacity do co-vary. This is explained as the mixing of relatively coloured river water rich in ligands with uncoloured seawater of low ligand concentration. DOC and complexation capacity in sewage effluent show a strong correlation that might form the basis of a predictive relationship.

Copper Complexation and Toxicity to Phytoplankton in the Huron River, a Lake Erie Tributary

The effect of speciation on the toxicity of copper to phytoplankton in the Huron River watershed was assessed by changing the copper complexation capacity in water samples and measuring the levels of chlorophyll a. Differences in strength of conditional stability constants (log K′) of coppercomplexes found in these samples (Ford Lake: 8.8 ± 0.3, Huron River: 10.3 ± 0.4) suggested that coppercomplexing ligands in Ford Lake were mainly derived from humic material, whereas in the lotic environment, they might have been biologically produced. Appearance of the voltammograms obtained for water samples from each of the environments indicated that different biological components predominated in these two ecosystems. Despite the relatively high copper complexation capacity observed when 51 nM of copper was added to water samples, adverse effects reflected as lowered chlorophyll a levels were observed in the phytoplankton, suggesting some buffering of the electrolabile copper at a critical safe dose.

Speciation of copper in sewage effluents and its toxicity to Daphnia magna

Copper complexation capacity was determined in a range of sewage treatment works final effluents and receiving waters, upstream and downstream of the discharge point. Forty-eight-hour immobilization tests on Daphnia magna were used to assess the toxicity of copper in the effluent matrix. Complexation capacities in effluents were typically in the range 50 to 100 microg Cu/L, with higher values being found in the poorer-quality effluents with higher dissolved organic carbon (DOC) concentrations. The tolerance of Daphnia to dissolved copper concentrations was more than quadrupled in a 50% effluent matrix, with the increase in tolerance being related to complexation capacity. Ligand concentrations in effluents were found to correlate strongly with effluent DOC. No such relationship was observed in surface waters. On mixing with river water, sewage-derived ligands behaved conservatively and were relatively stable over time scales of up to 10 d.

Interlaboratory comparability of copper complexation capacity determination in natural waters.

The results of a test of interlaboratory comparability for the determination of copper complexation capacity and copper-ligand complex formation constant are presented. Eight water samples comprising, six natural waters, a synthetic ligand solution and a blank solution were analysed by seven laboratories using their own methods of complexation titration. Given the wide variation that might have been possible, relatively good comparability was demonstrated amongst the variety of methods for determining copper complexation capacity. The complexation capacity data largely satisfied the predefined criterion of agreement to within 50%. This provides support for the use of metal speciation criteria in the regulation of copper in the environment. Data for the determination of complex formation constants were of poorer comparability, ranging between 10(7) and 10(12) for the same water.

Copper and mercury complexing capacity of organic matter from a mangrove mud flat environment, Sepetiba Bay, Brazil.

The biochem. of trace metals in mangrove environments has raised special attention due to the potential role of sediments in mangrove as both a sources and sinks for these pollutants. In the present study, we investigate the complexing capacity of org. matter in pore tidal waters, for two contrasting metals Cu and Hg, for which mangrove have been reported as a sink and source, resp. We hypothesize that post depositional changes in the org. matter are responsible for the different complexing capacities of org. matter, which results in a different migration pattern between Hg and Cu and in layer accumulation of Cu relative to Hg in mangrove environments. By using complexing capacity methods, some evidence was shown of different mechanisms of transport for Cu and Hg in mangrove systems. Org. matter from the mud flat surface is more able to transport Cu ions than the deep sediment surface, and inversely for Hg.

Copper and Mercury Complexing Capacity of Organic Matter From a Mangrove Mud Flat Environment, Sepetiba Bay, Brazil

Copper and Mercury Complexing Capacity of Organic Matter From a Mangrove Mud Flat Environment, Sepetiba Bay, Brazil

Etude de L'Influence Du Ver De Terre Lumbricus Terrestris Sur La Capacite Complexante De La Solution Du Sol Study of Earthworm Influence Lumbricus Terrestris on Soil Solution Complexation Capacity

Four soil samples highly contaminated with metals of urban and mine origin (SE1, SE2, SM1, SM2) and having different physico-chemical proprieties were selected to study copper complexation capacity (LT) of soil solution. The effect of Lumbricus terrestris on copper complexation capacity of soil solution was investigated on SE1 and SE2. The complexation capacity was estimated by amperometric titration of soil solution by copper. Free hydrated cation and labile complexes of copper were determined by DPASV. The results show that the copper complexation capacity variation depends on the physicochemical caracteristics of soils, particulary pH. Thus, the values of copper complexation capacity are 0; 0.6×10−7; 1.8×10−7 and 5.5×10−7 mol l−1 respectively for SM2; SM1; SE1 and SE2 which are pH 5; 5.4; 6.5 and 7.4. Based on these results, the bioavailability levels of heavy metals show the following pool ranking: SM2>SM1>SE1>SE2. The copper complexation capacity of soil solution increases with the soil disturbance by Lumbricus terrestris. This is more obvious when the time of disturbance by lumbrics is longer. Indeed, average values determined for 1 month and 3 months are 3.8×10−7 and 7.8×10−7 mol l−1 for SE1; 7.7×10−7 and 15.2×10−7 mol l−1 for SE2 respectively. It seems that the action of earthworm on soil can contribute to the decrease of bioavailability of heavy metals, particulary copper.